Apparatus and method for ultrasonic diagnostic imaging

ABSTRACT

An ultrasonic diagnosis apparatus and method wherein both imaging of a contrast effect and imaging of a tissue appearance before and after inflow of a contrast medium can be realized on condition that low-power transmission and a high frame rate are maintained. The ultrasonic diagnostic apparatus includes a transmission/reception unit for transmitting subject ultrasonic waves with a band substantially centered at a fundamental frequency and generating a received signal based on an ultrasonic echo from the subject, a harmonic unit for extracting a signal of a harmonic component of the fundamental frequency included in the received signal and extracting a signal of the fundamental component with the band substantially centered the fundamental frequency included in the received signal, and a display unit for generating a display image based on the extracted harmonic and fundamental components.

BACKGROUND OF THE INVENTION

[0001] Field of the Invention

[0002] This invention relates to an ultrasonic diagnostic apparatus, andparticularly to a contrast medium imaging technique.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2002-32770, filed Feb. 8,2002, the entire contents of which are incorporated herein by reference.

DESCRIPTION OF THE RELATED ART

[0004] Microbubbles contained in a contrast medium used for ultrasonicdiagnosis are collapsed by ultrasonic transmission and tend be collapsedwhen the transmitted sound pressure is higher. To maintain a contrasteffect, a certain measure needs to be taken such as imaging a contrastmedium while suppressing its collapse by using a low sound pressure(real-time perfusion image or RPI).

[0005] The case of extracting a second harmonic component of atransmitted fundamental wave from a received echo in RPI will now beconsidered. When the sound pressure is high, the second harmoniccomponent contains a nonlinear propagation component generated in thetissue.

[0006] When the sound pressure is low as in RPI, the nonlinearpropagation component generated from the tissue has very low intensity,which is insufficient for imaging. A tissue image can hardly be observedbefore inflow of a contrast medium, and only after inflow of thecontrast medium, a harmonic component due to the contrast medium beginsto appear.

[0007] In short, in the ultrasonic test using a contrast medium, whenthe sound pressure is lowered to maintain the contrast effect, anonlinear propagation component generated in the tissue has very lowintensity and therefore a tissue image hardly appears before inflow ofthe contrast medium. On the other hand, when the sound pressure israised to enable appearance of the nonlinear propagation componentgenerated from the tissue before inflow of the contrast medium, thecontrast effect momentarily disappears. Particularly, this problem isnoticeable at the time of ultra-low sound pressure driving where an MI(mechanical index) value, which is an index showing an output referenceobtained by normalizing a maximum peak negative sound pressure in atransmitted beam by the square root of the fundamental frequency, isapproximately 0.1.

[0008] To solve this problem, it may be conceivable to use aconventional color Doppler processing unit to prepare and display a Bmode with a fundamental wave as a tissue (background) image and todisplay a Doppler image (including phase inversion Doppler) as acontrast image. However, since separate transmissions and receptions arenecessary for the tissue and for the contrast, respectively, the framerate, which is particularly important for imaging a cardiovascularsystem, is lowered and the real-time property cannot be utilized.Moreover, the transmission for the tissue may cause unwanted collapse ofand adverse effects on the contrast medium.

[0009] When an image is generated using only a harmonic component with alow MI value, even if contrast-enhancement is performed, the brightnessof the image is low and it may be difficult to confirm the enhancedregion. If the gain is increased only to increase the brightness, noiseappears in the image. Even if the dynamic range is narrowed to brightena maximum brightness part, only a part having relatively high brightnessis emphasized and the contrast-enhancement cannot be correctlyevaluated.

BRIEF SUMMARY OF THE INVENTION

[0010] It is an object of this invention to realize both imaging of acontrast effect and imaging of a tissue appearance before and afterinflow of a contrast medium on condition that low-power transmission anda high frame rate are maintained in an ultrasonic diagnostic apparatus.

[0011] It is accordingly an aspect of the present invention to providean ultrasonic diagnostic apparatus, including a transmitter configuredto transmit a first ultrasonic wave and a second ultrasonic wave foreach scan line, the first and second ultrasonic waves having a commonpredetermined fundamental frequency in their frequency bands and atleast one different condition other than frequency; a receiverconfigured to receive first and second echo signals reflected from theobject body in response to the first and second ultrasonic waves,respectively, and to generate first and second reception signals basedon the first and second echo signals; a harmonic component extractingunit configured to extract a harmonic component of the fundamentalfrequency from the first and second reception signals; a fundamentalcomponent extracting unit configured to extract a fundamental componentfrom at least one of the first and second reception signals; an imageprocessor configured to produce the ultrasonic image based on theharmonic component and the fundamental component; and a displayconfigured to display the ultrasonic image.

[0012] According to another aspect of the invention, there is providedan ultrasonic diagnostic apparatus including a transmitter configured totransmitting an ultrasonic wave; a receiver configured to receive anecho signal reflected from the object body in response to the ultrasonicwave and to generate a reception signal based on the echo signal; afilter having pass bands such that a fundamental component and aharmonic component in the reception signal are extracted, respectively,wherein a relative intensity of the harmonic signal is larger than theintensity of the fundamental component; an image processor configured toproduce the ultrasonic image based on the harmonic component and thefundamental component; and a display configured to display theultrasonic image.

[0013] According to yet another aspect of the invention, there isprovided an ultrasonic diagnostic method including the steps oftransmitting a first ultrasonic wave and a second ultrasonic wave foreach scan line, the first and second ultrasonic waves having a commonpredetermined fundamental frequency in their frequency bands anddifferent conditions other than frequency; receiving the first andsecond echo signals reflected from the object body in response to thefirst and second ultrasonic waves, respectively, and generating firstand second reception signals based on the first and second echo signals;extracting a harmonic component of the fundamental frequency from thefirst and second reception signals; extracting a fundamental componentfrom at least one of the first and second reception signals; producingthe ultrasonic image based on the harmonic component and the fundamentalcomponent; and displaying the ultrasonic image.

[0014] According to yet another aspect of the invention, there isprovided an ultrasonic diagnostic method including the steps oftransmitting an ultrasonic wave; receiving an echo signal reflected fromthe object body in response to the ultrasonic wave and generating areception signal based on the echo signal; filtering the receptionsignal such that a fundamental component and a harmonic component in thereception signal are extracted, wherein a relative intensity of theharmonic signal is larger than the intensity of the fundamentalcomponent; producing the ultrasonic image based on the harmoniccomponent and the fundamental component; and displaying the ultrasonicimage.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0016]FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus ofan embodiment of the invention,

[0017]FIG. 2 shows a block diagram of a harmonic unit for a PhaseInversion/Filter method of the invention,

[0018] FIGS. 3A-3B are illustrations of an example of a set oftransmission ultrasound waves for a Pulse Inversion method,

[0019] FIGS. 4A-4B show spectrums of received signals in the PhaseInversion method,

[0020] FIGS. 5A-5B are illustrations of extracted harmonic andfundamental components in the Phase Inversion/Filter method,

[0021]FIG. 6 is a block diagram of a harmonic unit for the PhaseInversion method of the invention,

[0022]FIG. 7 is an illustration of processing in the Phase Inversionmethod,

[0023]FIG. 8 is a block diagram of a harmonic unit for a PulseModulation method using a filter,

[0024] FIGS. 9A-9B are illustrations of an example of a set oftransmission ultrasound waves for the Pulse Modulation method,

[0025] FIGS. 10A-10B show spectrums of received signals in the PulseModulation method,

[0026] FIGS. 11A-11B are illustrations of extracted harmonic andfundamental components in the Pulse Modulation method,

[0027]FIG. 12 is a block diagram of a harmonic unit for a Balance Changemethod of the invention,

[0028] FIGS. 13A-13B are illustrations of a process in the BalanceChange method,

[0029]FIG. 14 is a block diagram of a display unit of an embodiment ofthe invention,

[0030]FIG. 15 illustrates a process of a First Display mode of theinvention,

[0031]FIG. 16 illustrates a process of a Second Display made of theinvention,

[0032] FIGS. 17A-17B illustrate an effect of a synthetic image in theFirst and Second Display modes,

[0033]FIG. 18 illustrates a process of a Third Display mode of theinvention,

[0034]FIG. 19 illustrates a process of a Fourth Display mode of theinvention,

[0035]FIG. 20 illustrates a process of a Fifth Display mode of theinvention,

[0036]FIG. 21 illustrates a process of a Sixth Display mode of theinvention,

[0037]FIG. 22 illustrates a process of a Seventh Display mode of theinvention, and

[0038]FIG. 23 illustrates a process of an Eighth Display mode of theinvention,

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Referring now to the drawings, wherein like reference numeralsdesignate the same or corresponding parts throughout the several views,various embodiments of this invention will now be described.

[0040]FIG. 1 shows a structure of an ultrasonic diagnostic apparatusaccording to one embodiment. Reference numeral 11 denotes an ultrasonicprobe including plural transducer elements (electroacoustic transducerelements) arranged one-dimensionally or two-dimensionally and typicallyutilizing a piezoelectric effect. The ultrasonic probe 11 is connectedto an apparatus body 12 having a host CPU 14 as its main part, via aconnector, not shown. One or neighboring several transducer elementsconstitute one channel. It is now assumed that one transducer elementconstitute one channel. To the transducer elements of this ultrasonicprobe 11, transmission pulse voltage is applied from apulser/preamplifier unit 15 under a transmission condition that MI is0.6 or less. The transducer elements convert the electrical oscillationto mechanical vibration. This causes generation of ultrasonic waveshaving a frequency band centering a fundamental frequency ω1 from thetransducer elements. The pulser/preamplifier unit 15 provides a timedifference between channels with respect to the application timing ofthe transmission pulse voltage. This time difference (delay time) isprovided for focusing the ultrasonic waves generated from the pluraltransducer elements and for deflecting the focused ultrasonic waves. Bychanging this delay time, it is possible to arbitrarily change the focallength and the deflection angle (direction of transmission).

[0041] Ultrasonic waves are transmitted to a subject from the probe 11connected to the apparatus body 12. The ultrasonic waves are reflectedback to the probe 11 as an echo and are converted to electric signals bythe transducer elements. This echo includes a fundamental component of aband centered at the fundamental wave, and a harmonic component of aband centered at a frequency that is an integral multiple of thefundamental frequency, in this case, twice the fundamental frequency. Inthe case a contrast medium (microbubbles) has been injected in thesubject, nonlinear oscillation of the contrast medium generates aharmonic component. The echo of the contrast medium having thefundamental component centered at the fundamental frequency ω1 and theharmonic component centered at a frequency that is an integral multiple(twice or more) of the fundamental frequency is received by the sameprobe 11.

[0042] This electric signal is sent as a received signal to a harmonicunit 17 via the pulser-preamplifier unit 15, a reception delay circuit16 and a phase detector unit 19. Through this phase detection(quadrature detection), a carrier component becomes a DC componenthaving a phase. This phase detection processing may be performed in theharmonic unit 17. The reception delay circuit 16 is configured toperform beam forming (phasing addition processing) in reception andcontrolling the direction and convergence of an ultrasonic beam. Thereception delay circuit 16 may include plural circuit sets in order toform plural beams and simultaneously receive the ultrasonic beams inparallel. The received signal is sampled with a sampling frequencysuitable for signal processing and then converted to a digital signal,thus forming a beam.

[0043] The harmonic unit 17 generates harmonic image data from theharmonic component substantially centered at a frequency that is anintegral multiple (in this case, twice) of the fundamental frequencyincluded in the received signal, and also generates fundamental imagedata from the fundamental component substantially centered at thefundamental frequency included in the same received signal. These twotypes of image data generated by the harmonic unit 17, that is, theharmonic image data and the fundamental image data, are converted todisplay data of one frame by a display unit 18 and simultaneouslydisplayed on a monitor 13.

[0044] A characteristic feature of this embodiment is that the harmoniccomponent substantially centered at the frequency that is an integralmultiple of the fundamental frequency and the fundamental componentsubstantially centered at the fundamental frequency are extracted fromthe same received signal to generate harmonic image data and thefundamental image data, respectively, and simultaneously display thesedata.

[0045] With the harmonic image after inflow of the contrast medium, itsenhancement can be visually confirmed properly. Moreover, the low-powertransmission adjusted to such a level as to continuously maintain thecontrast effect has a problem that the harmonic component from thetissue has very low intensity before inflow of the contrast medium andthat the tissue appearance can hardly be visually confirmed, whereas inthis embodiment, since the fundamental image is generated using thefundamental component having signal intensity that is approximatelyseveral ten times or several hundred times that of the harmoniccomponent and the fundamental image is displayed together with theharmonic image, the tissue appearance can be confirmed using thefundamental image even before inflow of the contrast medium. Inaddition, since these two types of image data are generated from thesame received signal, the frame rate is not lowered. Furthermore, sinceincrease in brightness due to the contrast effect occurs both in theharmonic image and the fundamental image, the visibility of the enhancedpart is improved in comparison with the case of imaging with only theharmonic image.

[0046] In this embodiment, plural types of techniques to generateharmonic image data and to generate fundamental image data by theharmonic unit 17 are provided together with correspondingtransmission/reception techniques. One of these techniques may beemployed. Alternatively, all these techniques or an arbitrarycombination of these may be provided in the apparatus to enableselective use. The respective techniques will now be described in order.

[0047] (Phase Inversion/Filter Method)

[0048] In this phase inversion/filter method, a harmonic component isextracted by a phase inversion method, theoretically without including aresidual fundamental component, while a fundamental component isextracted by a filter. In the phase inversion method, transmission ofultrasonic waves and reception of echo are carried out twice on eachultrasonic scanning line. In one transmission, ultrasonic waves aretransmitted with a positive waveform as shown in FIG. 3A. In the othertransmission, ultrasonic waves are transmitted with a negative waveformas shown in FIG. 3B. In other words, there is a 180 degree phasedifference between the first and the second ultrasonic waves.

[0049]FIG. 4A shows the spectrum of a received signal received from thepositive transmission. FIG. 4B shows the spectrum of a received signalreceived from the negative transmission. As is already known, anonlinear phenomenon can be approximated as a square of the fundamentalwave. When the fundamental wave is expressed by a(t)sin ωt, thenonlinearity is approximated as (a(t)sin ωt)². Therefore, the harmoniccomponent is generated with the positive polarity both in positive andnegative transmissions, whereas the fundamental component is generatedwith the positive/negative polarity inverted depending on thetransmission polarity.

[0050] By adding the received signal due to the two positive andnegative transmissions at an adder 25 as shown in FIG. 2, it becomespossible to eliminate the fundamental component as shown in FIG. 5A andextract the harmonic component with its intensity substantially doubled.A filter using, as its passband, a band centered or substantiallycentered at a high frequency that is an integral multiple of thefundamental frequency or an arbitrary band may be arranged on thesubsequent stage of the adder 25, thus controlling the band for imaging.Meanwhile, in FIG. 2, the fundamental component is extracted from thereceived signal of the negative transmission pulse, using the filtermethod. However, the fundamental component may be extracted from thepositive-side signal.

[0051] (Phase Inversion Method)

[0052] In the above-described phase inversion/filter method, thefundamental component is extracted by a filter. However, the fundamentalcomponent may also be extracted by the phase inversion method.

[0053] Previously, utilizing the characteristic that the harmoniccomponent is constantly generated with positive polarity, thefundamental component is eliminated by adding the received signals ofthe two positive and negative transmissions at the adder 25, thusextracting the harmonic component. However, since the fundamentalcomponent is generated depending on the transmission polarity, theharmonic component may be eliminated by subtracting the received signalsof the two positive and negative transmissions at a subtractor 26, thusextracting the fundamental, as shown in FIGS. 6 and 7.

[0054] A filter using, as its passband, a band centered or substantiallycentered at the fundamental frequency or an arbitrary band may bearranged on the subsequent stage of the subtractor 26, thus controllingthe band for imaging.

[0055] (Pulse Modulation Method)

[0056] As is already known, a harmonic component has lower intensitythan a fundamental component. Under a transmission condition that MI is0.1 or less, a slight fundamental component is generated but littleharmonic component is generated. A technique to extract a harmoniccomponent using this characteristic is a pulse modulation method.

[0057] In the pulse modulation method, transmission and reception arecarried out twice on each ultrasonic scanning line. In one transmission,ultrasonic waves are transmitted with a relatively high amptitude (highsound pressure) as shown in FIG. 9A under a transmission condition thatMI is, for example, 0.6 or less. In the other transmission, ultrasonicwaves are transmitted with a relatively low amplitude (low soundpressure) as shown in FIG. 9B under a transmission condition that Ml is,for example, 0.1 or less.

[0058]FIG. 10A shows the spectrum of a received signal of a transmittedpulse with the relatively high amplitude. FIG. 10B shows the spectrum ofa received signal of a transmitted pulse with the relatively lowamplitude. In the transmission with the relatively high amplitude, thereceived signal includes a fundamental component and a harmoniccomponent. In the transmission with the relatively low amplitude, thereceived signal includes a fundamental component with low intensity anda harmonic component with extremely low intensity that is equivalent tozero.

[0059] By scaling the received signal of the transmitted pulse with therelatively low amplitude using a transmitted sound pressure ratio of thesound pressure with the high amplitude to the sound pressure with thelow amplitude (that is, multiplying the transmitted sound pressure ratioto equalize the reference amplitude) as shown in FIG. 8, and subtractingthe result from the received signal of the transmission with therelatively high amplitude at a post-amplitude-scaling subtractor circuit27, it is possible theoretically to eliminate the fundamental componentand extract the harmonic component, as shown in FIG. 11A.

[0060] Meanwhile, the fundamental component is extracted from thereceived signal of the transmitted pulse with the relatively highamplitude by the filter. Alternatively, the received signal of thetransmitted pulse with the relatively low amplitude after the scalingmay be passed through the filter 21.

[0061] (Balance Change Method)

[0062]FIG. 12 shows an exemplary structure of the harmonic unit 17corresponding to a balance change method in the above-describedtechniques, the harmonic component and the fundamental component areseparately extracted from the received signal, and also in the imagegeneration processing their respective image data are generated usingseparate parameters.

[0063] On the other hand, in the balance change method, by passing thereceived signal through a filter 28 for attenuating a band of afundamental component shown in FIG. 13A and relatively amplifying a bandof a harmonic component, it is possible to adjust the relative relationof intensity between the harmonic component and the fundamentalcomponent as shown in FIG. 13B and thus extract a noticeable contrastecho. The filter 28 uses a complex digital filter having an asymmetricfrequency passing characteristic. The passing rate of the fundamentalcomponent and the harmonic component can he arbitrarily changed using akeyboard 40, a volume control or the like on an operating panel. When anoperator changes a parameter related to the rate of the fundamentalcomponent and the harmonic component using the keyboard 40 or the likeon the operating panel, a filter coefficient corresponding to theparameter is set for the filter 28 under the control of a filtercontroller 41, thus changing the passing rate of the fundamentalcomponent and the harmonic component.

[0064] In this balance change method, it suffices to transmit andreceive ultrasonic waves only once on each ultrasonic scanning line anda high frame rate can be secured.

[0065] The balance change method can also be applied to the phaseinversion method. Specifically, after the intensity of the fundamentalcomponent is made lower than that of the harmonic component through afilter for attenuating the band of the fundamental component of one echosignal and relatively amplifying the band of the harmonic component,addition is performed.

[0066] As described above, in the techniques other than the balancechange method, the fundamental image data and the harmonic image dataare separately generated. Therefore, various variations can be providedfor image display. As typical display modes, eight types of displaymodes, that is, first to eighth display modes will be describedhereinafter. An operator can arbitrarily select one of these eight typesof first to eighth display modes.

[0067]FIG. 14 shows a structure of the display unit 18. Fundamentalimage data are converted to fundamental image data expressed by grayscale (hereinafter referred to as FG) by a frame memory 30 and a grayscale lookup table (LUT) 31 and then sent to an image processing unit32. Harmonic image data are converted to harmonic image data expressedby gray scale (hereinafter referred to as HG) by a frame memory 33 and agray scale lookup table 34 and then sent to the image processing unit32. The harmonic image data are also converted to harmonic image data ofcolor expression (hereinafter referred to as HC) by a color lookup table35 and then similarly sent to the image processing unit 32. The colorlookup table 35 assigns colors in accordance with the power value of theharmonic image data so that, for example, red is assigned for a smallpower value and color gradually changes to yellow as the power valueincreases.

[0068] The image processing unit 32 generates display data correspondingto a display mode designated by the operator, from these three types ofimage data FG, HC and HC. Scan conversion of the display data isperformed by a frame memory 36 on the output stage. The resultingdisplay data is passed through a digital analog converter (DAC) 37 andoutputted to the monitor 13. A number of display modes will now bedescribed in order.

[0069] (First Display Mode)

[0070] In the first display mode, as shown in FIG. 15, the imageprocessing unit 32 adds the gray-scale fundamental image data FG and thegray-scale harmonic image data HC pixel-by-pixel, thus generating oneframe of synthetic image data C1. This synthetic image data C1 isconverted by itself to one frame of display data.

[0071] Before inflow of a contrast medium, the tissue appearance can bevisually confirmed on the fundamental image. After inflow of thecontrast medium, the state of the inflow can be visually confirmedsatisfactorily on the harmonic image.

[0072] By adding the gray-scale fundamental image data FG and harmonicimage data HG, it is possible to reinforce the increase in brightnessdue to the contrast effect more effectively than in the case ofdisplaying the gray-scale harmonic image data HG alone, as shown in FIG.17A. Since the amount of increase due to the contrast effect of thefundamental component is added to the amount of increase due to thecontrast effect of the harmonic component in the displayed image, asshown in FIG. 17B, the increase in brightness is reinforced and thevisibility of the contrast range is improved.

[0073] (Second Display Mode)

[0074] In the second display mode, as shown in FIG. 16, the imageprocessing unit 32 partly synthesizes the gray-scale fundamental imagedata FG and the color harmonic image data HC, thus generating one frameof synthetic image data C2. Specifically, when the pixel brightness ofthe color harmonic image data HC exceeds 0 or its approximate value, thepixel brightness of the harmonic image data is selected as the pixelvalue of the pixel. When the pixel brightness of the harmonic image datadoes not exceed 0 or its approximate value, the pixel brightness of thefundamental image data is selected as the pixel value of the pixel. Inother words, in a region where the harmonic component is generated, theharmonic image is displayed, whereas in a region where the harmoniccomponent is not generated, the fundamental image is displayed.

[0075] By thus partly synthesizing the gray-scale fundamental image dataFG and the color harmonic image data HC, it is possible to visuallyconfirm the state of spatial spread of distribution of the harmoniccomponent (contrast medium) satisfactorily on the color image. Moreover,even before or after inflow of the contrast medium, the tissueappearance can be visually confirmed on the basis of the fundamentalcomponent in the region where the harmonic component is not generated.Since the harmonic component and the fundamental component havedifferent colors, these components can be easily identified.

[0076] (Third Display Mode)

[0077] In the third display mode, as shown in FIG. 18, the imageprocessing unit 32 arranges the gray-scale fundamental image data FG andthe gray-scale harmonic image data HG side by side within the samescreen.

[0078] By thus simultaneously displaying the gray-scale fundamentalimage data FG and harmonic image data HG side by side, it is possible toobserve both the distribution of the contrast medium (harmoniccomponent) and the tissue appearance (fundamental component). Therefore,before inflow of the contrast medium, the tissue appearance can beconfirmed mainly based on the fundamental image. After inflow of thecontrast medium, the contrast effect can be confirmed using both thefundamental image and the harmonic image.

[0079] (Fourth Display Mode)

[0080] In the fourth display mode, as shown in FIG. 19, the imageprocessing unit 32 arranges the gray-scale fundamental image data FG andthe color harmonic image data HC side by side within the same screen.

[0081] By thus simultaneously displaying the gray-scale fundamentalimage data FG and the color harmonic image data HC side by side, it ispossible to observe both the distribution of the contrast medium(harmonic component) and the tissue appearance (fundamental component).Therefore, before inflow of the contrast medium, the tissue appearancecan be confirmed mainly on the fundamental image. After inflow of thecontrast medium, the contrast effect can be confirmed using both thefundamental image and the harmonic image.

[0082] (Fifth Display Mode)

[0083] In the fifth display mode, as shown in FIG. 20, the imageprocessing unit 32 adds pixels of the gray-scale fundamental image dataFG and the gray-scale harmonic image data HG, thus generating syntheticimage data C1. The synthetic image data C1 and the grayscale fundamentalimage data FG are arranged side by side within the same screen.

[0084] By thus simultaneously displaying the synthetic image data C1 andthe gray-scale fundamental image data FG side by side, it is possible toimprove the visibility of the tissue appearance in addition to theeffect of the first display mode.

[0085] (Sixth Display Mode)

[0086] In the sixth display mode, as shown in FIG. 21, the imageprocessing unit 32 partly synthesizes the gray-scale fundamental imagedata FG and the color harmonic image data HC, thus generating syntheticimage data C2. The synthetic image data C2 and the gray-scalefundamental image data FG are arranged side by side within the samescreen.

[0087] By thus simultaneously displaying the synthetic image data C2 andthe gray-scale fundamental image data FG side by side, it is possible toimprove the visibility of the tissue appearance in addition to theeffect of the second display mode.

[0088] (Seventh Display Mode)

[0089] In the seventh display mode, as shown in FIG. 22, the imageprocessing unit 32 adds pixels of the gray-scale fundamental image dataFG and the gray-scale harmonic image data HG, thus generating syntheticimage data C1. The synthetic image data C1 and the color harmonic imagedata HC are arranged side by side within the same screen.

[0090] By thus simultaneously displaying the synthetic image data C1 andthe color harmonic image data HC side by side, it is possible to improvethe visibility of spatial distribution of the harmonic component, thatis, spread of distribution of the contrast medium, in addition to theeffect of the first display mode.

[0091] (Eighth Display Mode)

[0092] In the eighth display mode, as shown in FIG. 23, the imageprocessing unit 32 partly synthesizes the gray-scale fundamental imagedata FG and the color harmonic image data HC, thus generating syntheticimage data C2. The synthetic image data C2 and the color harmonic imagedata HC are arranged side by side within the same screen.

[0093] By thus simultaneously displaying the synthetic image data C2 andthe color harmonic image data HC side by side, it is possible to improvethe visibility of spatial distribution of the harmonic component, thatis, spread of distribution of the contrast medium, in addition to theeffect of the second display mode.

[0094] This invention is not limited to the above-described embodimentand various modifications can be effected at embodiment stages withoutdeparting from the scope of the invention. Moreover, the embodimentincludes various stages, and various inventions can be extracted bysuitable combinations of the plural constituent elements disclosedherein. For example, of all the constituent elements disclosed in theembodiment, some constituent elements may be deleted.

What is claimed is:
 1. An ultrasonic diagnostic apparatus for obtainingan ultrasonic image of an object body, comprising: a transmitterconfigured to transmit a first ultrasonic wave and a second ultrasonicwave for each scan line, the first and second ultrasonic waves having acommon predetermined fundamental frequency in their frequency bands andat least one different condition other than frequency; a receiverconfigured to receive first and second echo signals reflected from theobject body in response to the first and second ultrasonic waves,respectively, and to generate first and second reception signals basedon the first and second echo signals; a harmonic component extractingunit configured to extract a harmonic component of the fundamentalfrequency from the first and second reception signals; a fundamentalcomponent extracting unit configured to extract a fundamental componentfrom at least one of the first and second reception signals; an imageprocessor configured to produce the ultrasonic image based on theharmonic component and the fundamental component; and a displayconfigured to display the ultrasonic image.
 2. The ultrasonic diagnosticapparatus according to claim 1, wherein the first and the secondultrasonic waves are 180 degrees different in phase.
 3. The ultrasonicdiagnostic apparatus according to claim 2, wherein the harmoniccomponent extracting unit comprises an adder configured to extract theharmonic component by adding the first and second reception signals. 4.The ultrasonic diagnostic apparatus according to claim 2, wherein thefundamental component extracting unit comprises a subtractor configuredto extract the fundamental component by subtracting the second receptionsignal from the first reception signal.
 5. The ultrasonic diagnosticapparatus according to claim 2, wherein the fundamental componentextracting unit comprises a filter having a pass brand corresponding toa frequency band of the fundamental component and configured to extractthe fundamental component from one of the first and second receptionsignals.
 6. The ultrasonic diagnostic apparatus according to claim 1,wherein the transmitter is configured to transmit the first ultrasonicwave with a larger amplitude than that of the second ultrasonic wave. 7.The ultrasonic diagnostic apparatus according to claim 6, wherein theharmonic component extracting unit comprises: a scaling unit configuredto adjust the fundamental components of the first and second receptionsignals to be substantially the same in amplitude; and a subtractorconfigured to extract the harmonic component by subtracting the secondreception signal from the first reception signal after the adjustment.8. The ultrasonic diagnostic apparatus according to claim 7, wherein theharmonic component extracting unit further comprises: a filter having apass band corresponding to a frequency band of the fundamental wave andconfigured to extract the fundamental component from the adjusted secondreception signal.
 9. The ultrasonic diagnostic apparatus according toclaim 1, wherein, when an ultrasonic contrast medium containingmicrobubbles is injected in the object body, the transmitter isconfigured to transmit the first and second ultrasonic waves with an MIvalue such that the microbubbles are not substantially collapsed. 10.The ultrasonic diagnostic apparatus according to claim 9, wherein the MIvalue is less than 0.6.
 11. The ultrasonic diagnostic apparatusaccording to claim 1, wherein the image processor is configured toproduce a synthetic image by adding the harmonic component and thefundamental component.
 12. The ultrasonic diagnostic apparatus accordingto claim 11, wherein the image processor is configured to produce thesynthetic image to be displayed on the display in gray scale.
 13. Theultrasonic diagnostic apparatus according to claim 11, wherein the imageprocessor is configured to produce the synthetic image such that pixelscorresponding to the harmonic component are displayed in color andpixels corresponding to the fundamental component are displayed in grayscale.
 14. The ultrasonic diagnostic apparatus according to claim 1,wherein the image processor is configured to produce the ultrasonicimage with a harmonic image portion and a fundamental image portion tobe displayed on the display.
 15. The ultrasonic diagnostic apparatusaccording to claim 14, wherein the harmonic image portion is displayedin one of gray scale and color and the fundamental image portion isdisplayed in gray scale.
 16. The ultrasonic diagnostic apparatusaccording to claim 1, wherein the image processor is configured toproduce the ultrasonic image including a synthetic image portion,produced by adding the harmonic component and the fundamental component,and a fundamental image portion to be displayed on the display.
 17. Anultrasonic diagnostic apparatus for obtaining an ultrasonic image of anobject body, comprising: a transmitter configured to transmitting anultrasonic wave; a receiver configured to receive an echo signalreflected from the object body in response to the ultrasonic wave and togenerate a reception signal based on the echo signal; a filter havingpass bands such that a fundamental component and a harmonic component inthe reception signal are extracted, respectively, wherein a relativeintensity of the harmonic signal is larger than the intensity of thefundamental component; an image processor configured to produce theultrasonic image based on the harmonic component and the fundamentalcomponent; and a display configured to display the ultrasonic image. 18.The ultrasonic diagnostic apparatus according to claim 17, wherein aratio of the intensities of the fundamental component and the harmoniccomponent is adjustable.
 19. The ultrasonic diagnostic apparatusaccording to claim 17, wherein the filter comprises a digital complexfilter having an asymmetric frequency characteristic.
 20. The ultrasonicdiagnostic apparatus according to claim 18, further comprising: an inputunit configured to input a parameter for controlling said ratio; and anadjusting unit configured to adjust the ratio according to theparameter.
 21. An ultrasonic diagnostic method for obtaining anultrasonic image of an object body, comprising the steps of:transmitting a first ultrasonic wave and a second ultrasonic wave foreach scan line, the first and second ultrasonic waves having a commonpredetermined fundamental frequency in their frequency bands and atleast one different condition other than frequency; receiving the firstand second echo signals reflected from the object body in response tothe first and second ultrasonic waves, respectively, and to generatefirst and second reception signals based on the first and second echosignals; extracting a harmonic component of the fundamental frequencyfrom the first and second reception signals; extracting a fundamentalcomponent from at least one of the first and second reception signals;producing the ultrasonic image based on the harmonic component and thefundamental component; and displaying the ultrasonic image.
 22. Theultrasonic diagnostic method according to claim 21, wherein the firstand the second ultrasonic waves are 180 degree different in phase. 23.The ultrasonic diagnostic apparatus according to claim 21, wherein thestep of extracting the fundamental component comprises a step of addingthe first and second reception signals.
 24. The ultrasonic diagnosticapparatus according to claim 21, wherein the step of extracting thefundamental component comprises a step of subtracting the secondreception signal from the first reception signal.
 25. The ultrasonicdiagnostic method according to claim 21, wherein the step of extractingthe fundamental wave comprises a step of filtering one of the first andsecond reception signals such that a frequency band of the fundamentalwave passes.
 26. The ultrasonic diagnostic method according to claim 21,wherein the first ultrasonic wave has a larger amplitude than that ofthe second ultrasonic wave.
 27. The ultrasonic diagnostic apparatusaccording to claim 26, wherein the step of extracting the harmoniccomponent comprises the steps of: scaling the fundamental components inthe first and second reception signals to be substantially the same inamplitude; and subtracting the second reception signal from the firstreception signal.
 28. The ultrasonic diagnostic method according toclaim 27, wherein the step of extracting the harmonic component furthercomprises a step of filtering the second reception signal such that afrequency band of the fundamental wave passes.
 29. The ultrasonicdiagnostic method according to claim 21, wherein, when an ultrasoniccontrast medium containing microbubbles is injected in the object body,and the transmitting step comprises transmitting the first and secondultrasonic waves with an MI value such that the microbubbles are notsubstantially collapsed.
 30. An ultrasonic diagnostic method forobtaining an ultrasonic image of an object body, comprising:transmitting an ultrasonic wave; receiving an echo signal reflected fromthe object body in response to the ultrasonic wave and generating areception signal based on the echo signal; filtering the receptionsignal such that a fundamental component and a harmonic component in thereception signal are extracted, wherein a relative intensity of theharmonic signal is larger than the intensity of the fundamentalcomponent; producing the ultrasonic image based on the harmonicaomponent and the fundamental component; and displaying the ultrasonicimage.
 31. The ultrasonic diagnostic method according to claim 30,wherein a ratio of the intensities of the fundamental component and theharmonic component is adjustable.
 32. An ultrasonic diagnostic apparatusfor obtaining an ultrasonic image of an object body, comprising: atransmitter configured to transmit a first ultrasonic wave and a secondultrasonic wave for each scan line, the first and second ultrasonicwaves having a common predetermined fundamental frequency in theirfrequency bands and being 180 degree different in phase; a receiverconfigured to receive first and second echo signals reflected from theobject body in response to the first and second ultrasonic waves,respectively, and to generate first and second reception signals basedon the first and second echo signals; a harmonic component extractingunit configured to extract a harmonic component of the fundamentalfrequency from the first and second reception signals by adding thefirst and second reception signals; a fundamental component extractingunit configured to extract a fundamental component from at least one ofthe first and second reception signals; an image processor configured toproduce the ultrasonic image based on the harmonic component and thefundamental component; and a display configured to display theultrasonic image.
 33. The ultrasonic diagnostic apparatus according toclaim 32, wherein the fundamental component extracting unit comprises asubtractor configured to extract the fundamental component bysubtracting the second reception signal from the first reception signal.34. The ultrasonic diagnostic apparatus according to claim 32, whereinthe fundamental component extracting unit comprises a filter having apass band corresponding to a frequency band of the fundamental componentand configured to extract the fundamental component from one of thefirst and second reception signals.
 35. An ultrasonic diagnosticapparatus for obtaining an ultrasonic image of an object body,comprising: a transmitter configured to transmit a first ultrasonic waveand a second ultrasonic wave for each scan line, the first and secondultrasonic waves having a common predetermined fundamental frequency intheir frequency bands, and the first ultrasonic wave having a largeramplitude than that of the second ultrasonic wave; a receiver configuredto receive first and second echo signals reflected from the object bodyin response to the first and second ultrasonic waves, respectively, andto generate first and second reception signals based on the first andsecond echo signals; a harmonic component extracting unit configured toextract a harmonic component of the fundamental frequency from the firstand second reception signals by adding the first and second receptionsignals, comprising: a scaling unit configured to adjust the fundamentalcomponents of the first and second reception signals to be substantiallythe same in amplitude, and a subtractor configured to extract theharmonic component by subtracting the second reception signal from thefirst reception signal after the adjustment; a fundamental componentextracting unit configured to extract a fundamental component from atleast one of the first and second reception signals; an image processorconfigured to produce the ultrasonic image based on the harmoniccomponent and the fundamental component, and a display configured todisplay the ultrasonic image.